Method of manufacturing arsenate of lead.



E. 0. BARSTOW.

METHOD OF MANUFACTURING ARSENATE 0F LEAD.

APPLICATION FILED AUG. 1, 1912. p

- Patented Jan. 20, 1916.

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U 9 2 L z 4 Z i (f r J :\2 I 0" U 2 WITIVESSES= EDWIN O. BARS'IOW, F MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN.

METHOD OF MANUFACTURING ARSENATE OF LEAD.

Applicatiozi filed August 1,

To all whom it may concern:

Be it known that I, EDWIN O. BARs'roW, a citizen of the United States, and a resldent of Midland, county of Midland, and State of Michigan, have invented a new and useful Improvement in Methods of Manufacturing Arsenate of Lead, of which the following is a specification, the principle of themvention being herein explained and the best mode in which 'I have contemplated applying that principle, so as to distinguish it, from other inventions. v While the present invention is of principal interest in the manufacture on a commercial scale of lead .arsenate, either the normalarsenate, Pb,( AsO,) or the acid arsenate PbHAsO,, the general mode of procedure, as well as the several specific methods or processes involved, are equally applicable-to the manufacture of other insoluble arsenates than such lead arsenate, as

In said annexed drawings Figure 1 illustrates in diagrammatic fashion a typical apparatus such as maybe employed in carrylng on the various steps comprehended in the present improved process of manufacture; and Fig. 2 is a tabular exhibit of the different reactions which are assumed to occur in carrying on such process in the several modified ways hereinafter described.

The general method of procedure involved in the improved process under consideration consistsdn oxidizing an arsenic derivative which is desired as a final product.

toarsenic acid by means of a halogen, pro viding a compound to form a haloid withv such halogen reagent, and adding a suitable compound of. the metal, the arsenate K: preyiously indicated, the process is applicable to'any metal capable of being precipitated as such arsenatefrom its corresponding soluble salt, such as its haloid.

Commenting further on this statement rela-P actions; for on chlorinating the resulting solution, as represented by reactlon IV., the 110 tive to the general mode of procedure, it

Specification of Letters Batent.

Patented Jan. 25, 1916. 1912. Serial No. 712,676. M

should benoted that it-is immaterial, so far as the steps in the process are concerned, whether they be performed in the sequence ust indicated, or in part, or in whole, simultaneously; and, as will be presently explained, the provision of a. compound to go with the halogen reagent may, in a sense, be anticipated by adding the base employed for this purpose first, and oxidizing the arsenic derivative subsequently.

With regard to the several reactions exhibited in Fig. 2 of the drawings, it should be explained that these merely express the inventors understanding of what takes place, and while they are believed to be indicative of the principal phenomena, and to properly explain the'production of the end- I products obtained, the actual process or processes hereinafter described, are not conditioned upon the actual occurrence of these reactions. j

Reaction I. is intended to express what occurs when white arsenic or a'rsenious oxid (As O as the specific arsenic derivative of the general process previousl oxidized to arsenic acid by ei'ng treated with chlorin, as the s ecific halogen of such process, in the pres cc of water. There resultsa mixture of arsenic acid (H AsO and hydrochloric acid (HCl). acid solution an alkali, specificallysodiun'i carbonate or soda ash Na CO,) is then added in amount carrying base equivalent to the hydrochloric acid ,(HCl) contained in such solution. The solution thus obtilained may, for convenience, be assumed to e ar-.. senic acid and sodium chlorid or common salt (N aCl), as per reaction 111., but it is probable that arsenic acid, hydrochloric acid, sodium-arsenate and sodium chlorid are all present; as well as free ions of sodium, chlorin and AsO This same solu-' tion of arsenic acid and salt may be obtained by adding the alkali first, as has been already-suggested is possible, and as is indicated in reactionII. of the tabular exhibit,

Fig. 2. In this..case the arsenious oxid'is combined with soda ash, in-the presence of water, and inasmuch as no carbomc acid gas is apparently evolved, the reaction is 'believedto be correctly represented as given. .The exact intermedlate phenomena are however immaterial here as in the. 'other reoutlined, 'is 80 To this 85 end result is the same as in the case of combining reactions 1. and 111., namely the equivalent of a solution of arsenic acid and common salt is obtained.

Instead of using soda ash, orequivalent alkali, in the fashion illustrated in reactions 11. and 111., sodium arsenate (Na HASOQ,

or an equivalent soluble arsenate, may be used in quantity suflicient to furnish base equivalent to the halogen used, in which case the arsenic acid contained in such soluble arsenate. is liberated, the base uniting with v I the halogen to form a soluble haloid, as indicated by reaction XIV. Furthermore, a solution assumed to be arsenic acid and a soluble chlorid, equivalent to that produced by reactions 111. and 1V., may be obtained by adding hydrochloric acid to a solution of a soluble arsenate, this reaction being shown in. equation XV. in which sodium arsenate solution is treated with hydrochloric acid. The solution from any of these reactions may accordingly be used in the remaining step of the process, which consists in reactin with y the solution thus obtained on a suitable compound of the metal of which the arsenate is, desired. This remaining'step, referring for the sake of illustration to the case whereiit is lead arsenate that is wanted,

is carried out by adding to the solution resulting from reactions 111., IV., XIV. and

XV., respectively, an oxid, hydrate, carbonate, or basic carbonate of lead, as per reaction V., which illustrates the use of the I oxid, and assumes the significant reagnt inthe solution to be arsenic acid. The-result Where each of the other lead compounds just referred to are employed is illustrated in the "following reactions t 40 As ,an alternative to the reactions given above to represent what happens when the arsenious .oxid is chlorinated, the chlorin combined to form a chlorid, and an oxygen derirative of lead added to the resulting solution to form the desired arsenate,.the

following equations may be given 2H,'As0,+4HC1+2Na,GO,:

- HGl+2Na,HAsO +2GO +2I-1 O. 2HO1 Na,.HAsO 11 0 PbO PbCl Na HAsO +2H O=PbHAsO +2NaCl+ 2H,O. o i In other words, it is immaterial, so far as the reaction with the lead oxid is concerned, whether arsenic acid, 6r hydrochloric acid,

.or both, be assumed to be present; and in determining the amount of such oxid to be added, it suffices to determine the amount of free acid present without inquiring as to whichone it is.

The several preliminary reactions hereinbefore described may be conducted satisfactorily in suitable open tanks, or tubs, into which the white arsenic and water in reaction 1., or the white arsenic and soda ash and waterin reaction '11.,are charged, as

7 shown in Fig. 1; while the chlorination may take up the chlorin as fast as it is supplied,

andthe tank itselfbe usedsimply as a saturating tank; In order to utilize all of the chlorin gas being furnished to the chlorinating towers in said reaction I. or in reaction IV., it has been found best to conduct the chlorination in two steps or stages by providing two similar tank and tower units it with independent pumps, the gas being passed in series first through the tower of unit No. 2 and then through the tower of unit No. 1 and the raw materials being. charged intothe tank of the first unit and when partly chlorinated, being transferred to the second; This is the arrangement illustrated in Fig. 1, already referred to. The

charge in the first instance will in the meanwhile have been. fully chlorinated and is forwarded to the next step in the process.

-This arrangement permits the complete ab sorption of the chlorin by the'more active raw materials, when commercial chlorin containing some air is utilized for the proc:

ess, and also permits finishing the chargein the No. 1 unit without the escape of chlorin from the system. The lead oxid, or equivthe resulting solution of arsenic and hydrochloric acids, this operation being satisfactorily conducted in a wooden tank provided with a suitable stirrer, and with the solution so concentrated, that the resulting mass will have the consistency of a cream, or paste. It has been discovered that by sufficiently prolonging the stirring, the lead arsenate may be made from the solid lead oxid despite the fact that at first sight it 'alent oxygen derivative, is then added to. 1

would seem that this reaction could not be I carried to completiombecause, the resulting product being solid, all of the lead oxid would not be reacted upon, but particles of it would be inclosed in an impervious coat- 1 ing of the lead arseriate. By subjecting the mixture, however, to prolonged stirring, or agitation, this tendency has been successfully overcome, as above indicated.

It has further been discovered that if: instead of adding an alkali, such as the spdium carbonate previously referredto, to the products resulting from reaction I., a. suit-- I considerable length of time so that the lead oxid may become thoroughly converted to such lead chlorid, this operation being conducted in the presence of water insufiicient in amount to dissolve the lead chlorid that is formed. The solution of arsenic acid thus produced may then be separated from the solid lead chlorid, as by decantation or filtration, and used for the production of arsenate of lead by stirring with lead oxid, hydrate, carbonate, or basic carbonate, as in reaction XIII, which illustrates the use of the oxid, or as in reaction X., which illustratesthe use of the carbonate. Again, instead of adding an alkali, (whether in the form of sodium carbonate as illustrated in reactions II. and III., or in the formof sodium arsenate as illustrated in reaction XIV.), simply in quantity sufficient to furnish base equiva-' lent to the halogen used, the acid solution resulting from reaction I. may be completely neutralized with alkali in order to produce the normal arsenate of lead instead of the hibited in reaction XVI., the next step then being to stir lead chlorid (reaction XVII.)

' with the resulting solution with -the producess under discussion permits 0 tion of such normal Pb,(AsO,),.

Itwill thus be seen that the fgeneral procthe production of the acid arsenate of lead PbHAsO or of the normal arsenate Pb,(AsO,),,, in varying'amou-nts, as may be desired depending on how much of theorigin'a-l adid solution is deflected to the reactions 111., VI., and XVI. It should further be explained that preferably the lead oxid, hydrate, carbonate, or basic carbonate, where either of these is employed in the step resulting in the production of the arsenate, is not used in thelproportions of its combining weight with the arsenic acid present in the solution, but care is taken to not add suflicient lead compound to combine with all of such acid.

arsenate of lead,

.It has been discovered that by proceeding in this way an arsenate higher: in arsenic acid is obtained than if the materials be used in the proportions of their combining weights. This is a distinct advantage in the production of commercial arsenates.

.The lead chlorid used in reaction XVII. may be that separated out in reaction VI, or it may be derived in any other suitable way. So, too, the chlorid thus resulting from the reaction-last named may be employed in a further modification of the present general process by precipitating it as lead carbonate, or hydrate, by treatment with soda ash, or lime. This step is shown, in reaction VIII., and the lead carbonate, or hydrate, so formed canbe then used to produce lead arsenate by agitating'with a solution containing arsenic acid, as per equation X. the acid solution being produced by equation VI.; or such lead chlorid may be dissolved and precipitated as lead arsenate by reacting with a solution of a soluble arsenate as shown in equation XL, or otherwise used as desired.

The exact compensation of the lead arsenate obtainedin the reaction between lead chlorid and a soluble arsenate, as also its physical properties, are dependent upon the ratio of base to arsenic in the arsenate solution. \Vhen suflicient base is present, normal arsenate Pb,,,(AsO,,) is obtained, as per j equation XII, in the form of a flocculent,

slow settlingprecipitate, and when less base is present, a mixture of the normal and acid arsenate PbI-IAsO is produced in the form of a granular rapid-settling precipitate. Equation XI., as written, shows one reaction which occurs when not enough base is present to produce a normal arsenate.

Commercial sodium arsenate may be used to precipitate the lead arsenate, as above described, or a solution of a soluble arsenate may be obtained by adding alkali to any of the various solutions of arsenic acid pro duced by the reactions above described. .For instance, note reaction IX.', in which the arsenic acid from VI. after being separated as by filtration from the solid lead chlorid is neutralized with soda ash to produce a solution of sodium arsenate, which may then be utilized in carrying out the step exhibited in the reaction XII. just described. If, on the other hand, the mixture of arsenic acid solution and lead chlorid resulting from said reaction VI. be treated as it stands with sodium carbonate, the acid lead arsenate may be produced in a single step as represented by the reaction of equation VII.

While the inventor prefers in some cases to separate the solid lead chlorid and to dis solve it before precipitating as lead arsenate, because in this way he is enabled to remove the insoluble impurities from the chlorid, which may have come from the use ofan impure lead oxid and which would otherwise contaminate the final product, and further he is thereby enabled to obtain an arsethe lead arsenate.

nate having certain desirable physical qualities, yet he has discovered that the reactions given may be successfully conducted in the presence of water insufficient in amount to dissolve the lead chlorid, providing the mixture be stirred for a longer time than necessary where solutions are used, and if .a pure oxid, carbonate or equivalent be used, there.

will be no impurities requiring separation. This discovery enables him to conduct large scale operations of this nature in very much smaller tanks than if the lead chlorid, which is sparingly soluble, be dissolved, and a much larger output may be thereby obtained from a plant representing an equal investment. It would appear at first sight that such reactions could not be carried to completion because the resulting product,

being solid, all of the lead chlorid would not be reacted upon but particles of it would be inclosed in an impervious coating of The inventor has successfully overcome this tendency, as above announced, by subjecting the mixture to prolonged stirring or agitation.- This operation can be satisfactorily conducted in a wooden tank, provided with a suitable stirrer and with a solution so concentrated that the resulting mass will have the consistency of a thick cream. The inventor has further discovered that it is not necessary to separate the lead chlorid from the solution of arsenic acid, as obtained in reaction VI. but that arsenate of lead may be obtained di rectly by stirring the solid chlorid and arsenic solution with an alkali, as shown in reaction VII, and that in the presence of water insufficient to dissolve the lead chlorid and .even in such concentration as to produce a mass having the consistency of cream. This step requires also prolonged stirring, as described for the similar reactions when using the lead chlorid separately, and if a pure lead oXid be used, a satisfactory arsenate may be obtained. This step, conducted with the solid chlorid and arsenic acid solution, has the same advantage of large output in small tanks, as already noted herein.

The oxygen derivatives of lead, which are suitable for use as compounds of that metal for reacting with arsenic acid to form lead monly known to the trade as arsenate of lead; The latter term is accordingly to be understood as used in this general sense, and not "as referring specifically to either of the two arsenates named, except where the contrary is indicated.

It is proper to repeat, clusion, that the several equations of Fig. 2, which have been referred to as expressive of the different reactions involved, are presented as illustrativemerely of the principal phenomena. They do not, however, neces sarily represent all of the reactions that ocour, and should be understood as indicating how the desired end-product isv derived by way of con-' i rather than the exact intermediate steps leading up thereto. ,7

From thestandpoint of the manufacturer or practical chemist, it might be better to represent the wholeseries of detailed reactions pertaining to each particular process or sub-process described above, as a single comprehensive reaction, in which only the starting materials and observed end-prodw nets are given. Thus, for example, the specific mode of operation herein claimed may be represented as fpllows:'

J In other words, sofar as the commercial operationv of the process. in hand is concerned, it may be regarded as consisting in a reaction between whi arsenic," chlorin, soda ash, and lead oxi been indicated the soda ash is typical of any suitable compound capable of combining with the chlorin, and may be lead oxid or other oxygen derivative of lead.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the process herein disclosed, provided the step or steps stated by any one of the As has already, 1

following claims or the equivalent of such stated step or steps be employed. a s

I therefore particularly point out and (11S- tinctly claim'as my invention;'

1. The method f making an insoluble metallic arsenate, which consists in reactingin the presence of water between arsemou's oxid, a halogen, a compound to form a haloid with such halogen, and a compound of the metal of which the arsenate is desired, such last-named compound beingadapted Y to produce such arsenate upon being added to a solution of. arsenic acid. L 2. The method of making an insoluble metallic arsenate, which consists in reactlng in the presence of water between arsenious oxid, chlorin, a compound to form a chlorid with such chlorin, anda compound of the metal of which the arsenate is desired, such last-named compound being adapted to produce such arsenate upon being added to a solution of arsenic acid.

3. The method of making an insoluble metallic arsenate, which consists in reacting in the presence of water between arsenious oxid, chlorin, an alkali, and a compound of the metal of which the arsenate is desired, such last-named compound being adapted to produce such arsenate upon being added to a solution of arsenic acid.

4. The method of making an insoluble metallic arsenate, which consists in reacting in the presence of water between arsenious oxid, chlorin, an alkali, and an oxid of the metal of which the-arsenate is desired.

5. The method of making lead arsenate, which consists in reacting in the presence of water between arsenious oxid, a halogen, a compound to form a haloid with such halogen, and a lead compound, adapted to produce such arsenate upon being added to a solution of arsenic acid.

6. The method of making'lead arsenate, which consists in reacting in the presence of water between arsenious oXid, chlorin, a compound to form a chlorid with such chlorin, and a lead compound adapted to produce such arsenate upon being added to a solution of arsenic acid.

7. The method of making lead arsenate, which consists in reacting in the presence of water between arsenious oxid, chlorin, an alkali, and an oxygen derivative of lead adapted to produce such arsenate upon being added to a solution of arsenic acid.

8. The method of making lead arsenate, which consists in reacting in the presence of water between arsenious oxid, chlorin, an alkali, and lead oxid.

9. The method of making lead arsenate, which consists in treating arsenious oxid with chlorin in the presence of water, thereby roducing hydrochloric acid and arsenic aci adding sodium carbonate in amount substantially equivalent to such hydrochloric acid; and adding lead oxid.

10. In a method of making an insoluble metallic arsenate, the step which consists in reacting in the presence of water with arsenic acid on a suitable compound of the. desired metal, the amount of such compound used being insufiicient to combine with all the arsenic acid present.

11. In a method of making lead arsenate, the step which consists in reacting in the presence of water with arsenic acid on a suitable lead compound, the amount of such compound used being insufficient to combine with all the arsenic acid present.

12. In a method of making lead arsenate, the step which consists in reacting in the presence of water with arsenic acid on oxygen derivative oflead adapted to produce such arsenate therewith, the amount of such derivative used being insufficient to combine with all the arsenic acid present.

13. In a method of making arsenate, the step which consists in reacting in the presence of water with arsenic acid on lead oxid, the amount of such oXid used being insufiicient to combine with all the arsenic acid present.

14:. The method of making lead arsenate, which consists in treating arsenious oxid with chlorin in the presence of water, therebyproducing hydrochloric acid and arsenic acid; adding sodium carbonate in amount substantially equivalent to such hydrochloric acid; and adding lead oxid in an amount insuiiicient to combine with all such arsenic acid.

Signed by me this 27 day of Jul 1912.

EDWIN 0. BAR TOW.

Attested by- A. N. PATRIARCH, LEO W. LOWE. 

